The present invention relates to bearing systems and, more particularly, to journal and pilot bearings with improved performance and longer lifetime characteristics. The bearing system of the present invention is especially adapted for use on that type of rock bit popularly known as a three cone bit; however, its use is not restricted thereto and the bearing system of the present invention can be used in other equipment wherein an improved bearing system is required.
A rotary rock bit must operate under very severe environmental conditions and the size and geometry of the bit is restricted by the operating characteristics. At the same time, the economics of petroleum production demand a longer lifetime and improved performance from the bit. In attempting to provide an improved bit, new and improved materials have been developed for the cutting structure of the cones thereby providing a longer useful lifetime for the cones. This has resulted in the bearing system being first to fail during the drilling operation. Consequently, a need exists for an improved bearing system to extend the useful lifetime of the bit.
In order to obtain high penetration rates with a rotary rock bit in some formations, it is necessary to apply heavy loads on the bit and to operate the bit at a moderate speed. With other formations only moderate loads are required but the bit must be operated at relatively high speeds. The rock bit operates under a highly corrosive environment and is subjected to temperature extremes. The drilling operation may be conducted thousands of feet underground wherein elevated temperatures are encountered. The bit is continually flushed by a circulating drilling fluid to cool the bit and carry away the drill cuttings. This fluid is generally water with chemicals added to control water loss or to control viscosity and/or pH. Some of these chemicals may result in a corrosive drilling fluid. The drilling cuttings, the materials encountered in the earth formations, barites added for fluid weight control, and the chemical composition of the drilling fluid combine to create a corrosive and abrasive drilling environment.
The bit is subjected to a wide range of fluid pressures during the drilling operation. When the bit is at the surface, it is of course only subjected to atmospheric pressure; however, when lowered into the well bore, it will be exposed to very high fluid pressure because of the head of the fluid in the well bore. In view of the circumstances explained above, it can be appreciated that a bearing system for a rotary rock bit must include exceptional performance characteristics in a limited geometrical configuration. Since the entire drill string must be withdrawn to replace the bit when it fails, it is highly desirable to have the bearing system operate for an extended period of time.